Final answer:
In humans, blood type is determined by three alleles: A, B, and O, but each individual can only have two because they inherit one allele from each parent. The correct answer to why this occurs is that each parent contributes one allele. This mechanism ensures genetic diversity while maintaining the diploid nature of individuals.
Explanation:
Understanding Human Blood Types
Human blood types are determined by the presence of specific alleles: A, B, and O. Each person inherits two alleles for blood type, one from each parent. This is due to the fact that individuals are dipoid, meaning they have two sets of chromosomes, which correspond to receiving one allele from each parent.
Why Only Two Alleles?
The correct answer to why only two of these alleles are present in an individual is: A Each parent only contributes one allele. During reproduction, alleles from each parent combine to determine the offspring's blood type. For example, if one parent has blood type A (genotype AO) and the other has blood type B (genotype BO), the possible blood types for their children could be AB, A, B, or O, depending on the combination of alleles inherited.
This genetic mechanism highlights how traits are inherited and helps explain the diversity of blood types in the population. The incorrect options you've provided can be explained as follows:
- B Each allele must be dominant or recessive: This statement is misleading. While some alleles can be dominant or recessive, not all traits follow simple dominance patterns. For blood type, A and B are codominant, while O is recessive to both.
- C Blood types are not separated during meiosis: This is inaccurate. During meiosis, alleles are segregated so that each gamete (sperm or egg) receives only one allele from each genetic pair.
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